Marie Colvin, who has been killed by a shell in Syria aged 56, was a fearless but never foolhardy war correspondent who believed passionately in the need to report on conflicts from the frontline. In a career spanning 30 years, she covered wars from around the world for the Sunday Times and was renowned for her compassionate, clear writing.

She was committed to reporting on the realities of war, especially the effects on civilians. That was exactly what she was doing in the beleaguered city of Homs at the time of her death. She had broadcast the day before and written movingly in her newspaper a few days earlier of the slaughter she observed as Syrian government forces continued to bombard the city.

In Sri Lanka in 2001, while covering the conflict between government forces and the rebel Tamil Tigers, Marie was struck by shrapnel. Undaunted by the loss of her left eye, she wore a black eye-patch from then on, which became something of a trademark. When I interviewed her shortly afterwards, she told me how she had walked 30 miles through jungle with her Tamil guides to evade government troops, an example of the effort she put into her work.

It was after the loss of her eye that she spelled out her reason for covering wars. She wrote of the importance of telling people what really happens and about "humanity in extremis, pushed to the unendurable". She continued: "My job is to bear witness. I have never been interested in knowing what make of plane had just bombed a village or whether the artillery that fired at it was 120mm or 155mm." She wrote about people so that others might understand the truth.

Marie sometimes did more than merely write. In 1999, in East Timor, she was credited with saving the lives of 1,500 women and children who were besieged in a compound by Indonesian-backed forces. She refused to leave them, waving goodbye to 22 journalist colleagues as she stayed on with an unarmed UN force in order to help highlight their plight by reporting to the world, in her paper and on global television. The publicity was rewarded when they were evacuated to safety after four tense days.

This was the essence of Marie's approach to reporting. She was not interested in the politics, strategy or weaponry; only the effects on the people she regarded as innocents. "These are people who have no voice," she said. "I feel I have a moral responsibility towards them, that it would be cowardly to ignore them. If journalists have a chance to save their lives, they should do so."

The people of East Timor did not forget their saviour. At the end of her Sunday Times report about her Sri Lankan experience, she wrote: "What I want most, as soon as I get out of hospital, is a vodka martini and a cigarette." Later that week, having moved briefly to a New York hotel, she was woken by a room-service waiter bearing a tray with a huge bottle of vodka and all the ingredients for her drink of choice. She discovered it had been "fixed, God knows how, by the East Timor crowd, the people in the compound".

Marie covered conflicts wherever they broke out – in the Balkans, notably, and in Chechnya and Zimbabwe – but she was particularly knowledgable about the Arab countries. She was therefore on hand to witness the 2011 revolutions in Tunisia, Egypt and Libya. In fact, the Libyan dictator, Muammar Gaddafi, had taken something of a shine to Marie during her first visit to Tripoli in the 1980s and she was obliged to shake off his unwelcome attention.

One of my earliest tasks when I joined the Sunday Times in 1987 was to contact Marie in Libya using a telex machine, because no telephone worked. She skilfully managed to write a coded piece that avoided the censor's pencil. It was my first glimpse of the dedication and determination that was the hallmark of her work. These were characteristics that, in the following years, saw her acknowledged by her peers as Britain's foremost war correspondent.

Marie was from an Irish background, born and raised in Oyster Bay, New York. She studied marine biology at Yale before switching to major in English literature while working on the university's paper. From that moment on, she told me, she was hooked on journalism.

After a year on a trade paper, she was hired by the international news agency UPI, working in New York and Washington before being transferred to France to become the Paris bureau chief. "It was a grand name for a one-woman band," she later recalled. But it provided her with the opportunity to cover the Middle East, and she soon became fascinated by the region's culture, politics and conflicts.

While there, she acted as a stringer for the Sunday Times and, in 1986, when the paper lost its renowned Middle East correspondent David Blundy to the Sunday Telegraph, Marie took his job. Blundy was to die two years later when caught in crossfire in San Salvador. Marie worked for the Sunday Times ever after, becoming the paper's foreign affairs correspondent in 1995, an acknowledgment of her wider role.

She was twice named foreign reporter of the year (2001 and 2010) in the British Press Awards. She was given an International Women's Media Foundation award for courage in journalism for her coverage of Kosovo and Chechnya. And the Foreign Press Association named her as journalist of the year in 2000.

She wrote and produced documentaries, including Arafat: Behind the Myth for the BBC in 1990, and she featured in the 2005 documentary film Bearing Witness with four other female war reporters.

Marie was married twice to the writer and journalist Patrick Bishop. Both marriages ended in divorce. She was also married to the Bolivian journalist and writer Juan Carlos Gumucio, who killed himself in 2002.

Maggie O'Kane writes: On the night of 21 February, the ITV news report from Homs had the voice of a calm, even-paced American journalist. It was a brief clip of Marie Colvin, maybe 30 seconds, in the middle of the world's most dangerous live war zone: "The Syrians are not allowing civilians to leave … anyone who gets on the street is hit by a shell. If they are not hit by a shell they are hit by snipers. There are snipers all around on the high buildings. I think the sickening thing is the complete merciless nature. They are hitting the civilian buildings absolutely mercilessly and without caring and the scale of it is just shocking."

The following morning I listened for her voice again on BBC Radio 4's Today programme, but she was not there. By then her body was in the rubble of a house that had suffered a direct hit from a Syrian government shell.

The first time I saw Marie, more than 20 years ago, she was walking through the lobby of the Al Rashid hotel in Baghdad, all curly hair and poise. She was 34 and the Sunday Times Middle East correspondent. She was also at the top of her career, where she would stay on and off for the rest of her life. She was never outshone by the others.

In Baghdad in 1991, in the days before the first Iraq war, there was the usual evacuation of journalists urged by their embassies to leave; controlled panic as the silver boxes of camera equipment were piled up in the lobby in preparation for that last flight out; low-intensity psychological warfare as journalists tried to scare each other: "You're not thinking of staying are you?" – translated as, "don't stay behind when I'm too scared".

But Marie seemed to be above it all, bustling back and forward, gathering bottled water, dried biscuits, tins of fruit and packs of Marlboro cigarettes and always some good whiskey. She came back with a canary for her room in the almost empty hotel. There had been some talk of biological weapons being used, but Marie's canary was her joke and her way of coping.

It was also Marie who stayed behind during the exodus of journalists from East Timor in 1999, refusing to leave the UN compound in Dili and reporting the terror, almost hourly, of the women and children inside. She flew back to Darwin, Australia, and I remember trying to say something profound to her about her bravery. "What about some lunch?" she said, brushing it all aside. She was the bravest woman I have ever known.

• Marie Catherine Colvin, journalist, born 12 January 1956; died 22 February 2012